1. Field of the Invention
The present invention relates to a recording and reproducing apparatus provided with a tracking servomechanism based on an optical means. More particularly, the present invention relates to a recording and reproducing apparatus that can perform precise tracking servo control by reducing the influence of noise contained in detected servo signals and a recording medium used for use in the recording and reproducing apparatus.
2. Description of Related Art
Magnetic tape, which is an example of a recording medium, is used for various purposes, such as audiotapes, videotapes, and computer tapes. Particularly, in the field of tapes for data backup, data backup tapes with storage capacities of several hundred GB per reel are being produced commercially as the capacities of hard disks to be backed up increases. Thus, increasing the capacities of backup tapes is essential for supporting further increases in the capacities of hard disks in the future.
Approaches for increasing the capacity of a recording medium include a method of increasing the linear recording density, a method of increasing the track density, a method of increasing the recording area, and a method of improving the recording efficiency through signal processing. Generally, these methods are combined so that an optimal balance is achieved.
In the method of increasing the track density, a technique to ensure the positioning accuracy of a recording and reproducing head by means of closed loop control based on a tracking servo has been established. In an optical servo, which is an example of the tracking servo, servo signals formed by grooves or concavities/convexities are provided on a data recording surface or a surface opposite to the data recording surface. These servo signals are irradiated with a laser beam, reflected light from the servo signals is photoelectrically converted to obtain electric signals, and tracking control is performed based on the obtained electric signals (for example, JP H11-339254A).
On the other hand, in a recording and reproducing apparatus based on a rotating head system, recording/reproduction tracks are obliquely provided on a recording surface of a magnetic tape. In this configuration, there is proposed a recording and reproducing apparatus in which recording tracks are made to wobble and tracking servo signals are obtained by synchronously detecting reproducing signals during reproduction so that a reproducing head can accurately follow on the recording tracks (for example, JP S60-43216A).
However, in recent data media with increased capacities, the data track width has been narrowed, or in other words, the track density has been increased, and the recording density when writing data has been increased. To cope with this trend, servo signals are also required to be of extremely high precision. For example, in recording and reproducing apparatuses employing optical servos, concavities/convexities of servo signals provided on a recording surface are made finer.
For this reason, electric signals obtained by detecting reflected light from concavities/convexities become extremely weak, so that with conventional detecting methods, the signal-to-noise ratio decreases, and there is a problem that accurate tracking servo control is difficult.
Moreover, tapes of recent years have extremely large capacities, such as 1 TB or more, and also have extremely narrow data track widths, of the order of 5.0 μm. In addition, servo pits for generating servo signals are accordingly formed more densely or the servo pit area itself is reduced, and thus more complex servo signals are used. Therefore, performing servo tracking precisely is a major issue, and there is a need for a method that can cope with a further increase in the data capacity in the future.
Moreover, the tracking servo system proposed in JP S60-43216A, in which system recording tracks are made to wobble, is a totally different servo system from the optical servo, which is based on reflected light from servo signals. Thus, JP S60-43216A does not propose any improvement of the precision in optical servos.